1. Field of the Invention
The invention disclosed herein relates to radiation detectors, and in particular to radiation detectors integrated with downhole tools useful for evaluating sub-surface materials.
2. Description of the Related Art
Current techniques used for exploration and production of hydrocarbons call for performing various types of subterranean surveys. In order to complete such surveys, a borehole is typically drilled into the earth and through sub-surface materials that make up geologic formations.
Well logging is used to perform measurements of properties of the sub-surface materials penetrated by the borehole. Generally, a logging tool is attached to or included within a drill string. The drill string rotates to turn a rotary cutting device used to provide the borehole. In one embodiment, referred to as “logging-while-drilling,” the logging tool is used to perform the measurements during drilling or during a temporary halt in drilling.
Various types of measurements can be performed using such a logging tool. In general, various types of radiation sources (such as a pulsed neutron generator (PNG), a neutron source, a chemical source (e.g., a Cs-137 source), and other such sources) may be included in the logging tool or drill string to create particular types of radiation fields downhole. Some embodiments of logging tools simply monitor ambient radiation and are therefore “sourceless.” These logging tools all include some form of radiation detection equipment.
Common to each type of radiation detection instrumentation used in logging tools are various structural components. For example, a housing may be provided which contains the detection instrumentation and in turn lets manufacturers load the instrumentation into the logging equipment. Protection elements, such as suspension or vibration dampening components, as well as insulation and the like, may be included. As one might surmise, including housing and other components can lead to scatter and attenuation of radiation signals thereby reducing the performance of the detection instrumentation. Further, shielding of background radiation may be required by the measurement and not be provided by the housing, insulation, and suspension systems.